The present invention relates to a steering apparatus for turning the steerable wheels of a vehicle in response to rotation of a vehicle steering wheel.
Power steering gears are common in modern vehicles. Typically, one or more rigid shafts connect a vehicle steering wheel to an input shaft of the power steering gear. The rigid shafts must be routed from the vehicle steering wheel to the input shaft of the power steering gear. Routing the rigid shafts between the steering wheel and the steering gear is often difficult, as other vehicle components must not interfere with the shafts.
Some known vehicle steering systems have eliminated the rigid shafts. Such systems are commonly referred to as xe2x80x9csteer-by-wirexe2x80x9d systems. In steer-by-wire systems, there is no mechanical connection between the steering wheel and the steering gear. Instead, an assembly associated with the steering wheel sends an electronic signal to an assembly associated with the steering gear. The electronic signal actuates the steering gear. Since steer-by-wire systems have no mechanical connection, routing of the rigid shafts between the steering wheel and the steering gear is avoided. However, with no mechanical connection, steering control of the vehicle is lost if the steer-by-wire system fails.
The present invention is a steering apparatus for turning steerable wheels of a vehicle in response to rotation of a vehicle steering wheel. The apparatus comprises a first assembly, a second assembly, and a mechanism. The first assembly is operatively coupled to the steering wheel. The first assembly includes components for monitoring applied torque and angular rotation of the steering wheel and for transmitting a first signal indicative of the applied torque and angular rotation of the steering wheel. The second assembly includes a steering gear for, when actuated, turning the steerable wheels of the vehicle and components for receiving the first signal and actuating the steering gear in response to the first signal. The mechanism has first and second modes of operation. The mechanism, when in the first mode of operation, provides a mechanical connection between the steering wheel and the steering gear for enabling manual actuation of the steering gear. When the mechanism is in the second mode of operation, the steering wheel and the steering gear lack a mechanical connection for enabling manual actuation of the steering gear.